I have another cab for my 57 Chevy pickup that I have been working on for a while and I am looking for some suggestions on repairing rust on a section of the upper firewall where the cowl and firewall is spot welded together.
This cab was dipped in large tank of chemical stripper years ago so everything was stripped clean. My problem is where the cowl and firewall spot weld together it's rusting again and the rust is pushing the 2 layers sheetmetal apart between the spotwelds. Any ideas short of drilling the spotwelds and cutting out and replacing with new metal ?
Gene

Took a close look at the pictures you posted, don't know as I would be cutting out my firewall and installing a new one just yet. From what I see if you were to gently sand blast the area and tap with a welding hammer to locate any soft areas. Cut out the offending area and welding a patch with the proper gage metal and then treat and prime with an epoxy primer. An additional thing to take of would be the backside, sand blast and prime, followed by the application of seam sealer.
Hope this is helpful. Would most likely be easier,cheaper and you maintain the OEM firewall and all the specific holes and structure designed by GM. The replacement of the firewall does look real nice, but presents many other challenges particularily for structure and strength.
Best of luck which ever way you decide to go.
lowbux

My take on it is that your Rust could be the result of the dipping, and that panel appears to be a lap weld-a great place for the chemicals from dipping to hide-it is very difficult to completely neutralize dipping Chemicals. I would either replace, seperate, re-neutralize or replace that metal-I think your fight to keep Paint in that area has just begun-do you have any other areas showing this?

35window
Your take on this is right on the money. The cab was primed after it was dipped then while it was uncovered in my backyard it got rained on once , thats when I started noticing where the water reactivated the chemical in the overlap spot welded seams was rusting in between and running out of the seams. There are a few other spots that are easier to fix and then seam seal. I was thinking of drilling out the spot welds then cut out about a 1 1/2 inch strip all the way across and kill the rust then weld in a new piece.
I like the look of the stock firewall and I am in the process of welding up all the holes in it.
Gene

Well, let's take this one more step-now that we know this was stored outside, it looks to me that you used a standard Primer (read: porous), that may have contributed to your problem-either way, it sure wouldn't hurt to know what's in between those panels-I'm kinda worried about that pinch weld too-

It may be better in the long run to make a bigger piece(s) to replace those (less Heat=less distortion)-either way, Epoxy Primer is your friend-

By the way, unless you are looking for a "period" look, you could possibly use one piece to fill in the gap and butt weld it-just a thought-

I bought the cab along with some other pieces from the guy that had it stripped, I don't know what he used for primer. The pinch weld lip that runs across the firewall is two pieces. The bottom part of the firewall comes up and has a 90 degree bend that fits under the inner cowl piece that comes out and has that rolled over edge on it, I think that may be ok.
I was thinking of welding it all up from the inside where the 2 panels come together then cutting off the pinch weld lip and smoothing the upper part of the firewall. I'm still pondering that, mean while i'm welding up all the holes.
Gene

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